The invention relates to gas turbine engines and more particularly to a compressor casing insert.
It is known to improve the surge margin of a gas turbine engine compressor by applying a casing treatment to the casing wall, otherwise modifying the casing wall, in the vicinity of the tips of a rotary stage to remove or modify the behaviour of boundary layer airflow in the vicinity of the rotor blades. By this means the condition of compressor stall or compressor surge is alleviated or prevented from developing. A common factor in treatments of this kind is the provision of means that allows boundary layer circulation in circumferential or axial directions or both. Such means essentially comprises a flow path let into the casing wall with open access to the boundary layer on the compressor stage wall.